The invention relates to a bioreactor which has a reaction container for a substance to be acted upon with a medium and a pump for conveying the medium.
Nowadays one frequently speaks of bioreactors when one speaks about the field of xe2x80x9ctissue engineeringxe2x80x9d. A prominent goal in this field is to produce biological substitutes for damaged tissue or organs. But there is still a large number of other goal fields; for example the effectivity or toxicity of pharmaceutica can be tested using tissue of this kind, which can eliminate the future need for a large number of animal experiments and/or clinical experiments on humans.
Bioreactors are used in the production of tissue of this kind. In this the most diverse of reactor types are used, such as for example the so-called hollow fiber reactors. A hollow fiber reactor of this kind is known for example from U.S. Pat. No. 5,622,857. This reactor comprises a reaction container, through which a centrai strand of porous hollow fibers extends, through which a nutrient solution is pumped. This central strand of hollow fibers is concentrically surrounded by a plurality of strands of hollow fibers, through which a gaseous medium is conveyed. The hollow fibers of these strands are also constituted in such a manner that the gaseous mediumxe2x80x94for example oxygen or carbon dioxidexe2x80x94can at least partly emerge from these strands or enter into these strands respectively.
A cavity is in each case formed, both between the central strand and the strands surrounding this central strand as well as between these strands surrounding the central strand and the container wall. There the substancexe2x80x94e.g. parent cells or whateverxe2x80x94which is to be acted upon with the various media can be made available, where appropriate on a so-called xe2x80x9cmicro-carrierxe2x80x9d or a biodegradable matrix material. The nourishing of the substance takes place through the liquid nutrient solution, which can emerge to a certain extent from the pores of the central strand, and its provision with oxygen takes place through the gaseous medium.
Since as a rule the nutrient solution which again emerges from the reaction container is recirculated and used again for the next run, supplemented where appropriate by further nutrient solution, a xe2x80x9ccontaminationxe2x80x9d can of course easily occur. This is important insofar as these parts must be very intensively sterilized for the tissue of another patient in order that a contamination cannot arise. In spite of any sterilization of the individual parts, however intensive, a hundred percent sterilization cannot always be ensured. The sterility is however of central importance for the success of the xe2x80x9ctissue engineeringxe2x80x9d.
For the reaction container and for the supply lines a new reaction container and new supply lines respectively are already used in every employment.
But the pump can also be contaminated in employments of this kind. Since considered from the point of view of expenditure, the pumps are devices which still involve great expense, the latter are sterilized with a relatively great expenditure.
The present invention is dedicated to this disadvantage. An object of the invention is to propose a bioreactor in which the sterility can be ensured with great reliability in order not to endanger from the beginning the success of a xe2x80x9ctissue engineeringxe2x80x9d process which is to be carried out with this reactor for lack of sterility; on the other hand the expenditure for this should be as low as possible.
This object is satisfied in accordance with the invention by providing the bioreactor with an expendable pump.
In particular the pump for the conveying of the medium and/or, respectively, parts of the pump are designed as expendable or disposable parts. Through this the sterilization of the pump involving great expense is omitted.
In an advantageous exemplary embodiment the expendable parts of the expendable pump are manufactured of a plastic, since parts of this kind can be economically manufactured with great reliability, for example through injection molding processes.
In a further advantageous exemplary embodiment the expendable pump comprises a pump housing in which the pump wheel is arranged as well as a separate drive stator into which the pump housing together with the pump wheel which is arranged therein can be inserted. In this the housing together with the pump wheel which is arranged therein is designed as an expendable part. This exemplary embodiment is particularly advantageous insofar as all xe2x80x9ccontaminatable partsxe2x80x9d, namely the pump housing (inner wall) and the pump wheel which is arranged therein, can be replaced after every employment in the simplest manner, and the complicated and expensive parts (electrical supply of the drive, etc.) can be maintained and reused for the next employment without any danger of contamination existing. Furthermore, the electrical drive represents the most complicated and expensive part of the pump not only from the technical, but also from the economical point of view. The latter need however not be replaced, but rather only the less complicated and expensive pump housing with the pump wheel which is arranged therein.
In an advantageous further development of this exemplary embodiment permanent magnets are arranged in the pump wheel which then, together with the electromagnetic field which is produced by the drive stator, drive the pump wheel.
In an advantageous manner the expendable pump can be designed as a gear pump. This is a constructionally particularly simple type of pump which is also very economical to manufacture. Furthermore, gear pumps do not display the fatigue phenomena such as for example squeezed tube pumps, which are otherwise frequently used in such applications.
The bioreactor can for example be designed as a hollow fiber bioreactor, as has already been explained initially with reference to a special exemplary embodiment.
The bioreactor can however also be designed as a so-called airlift reactor (xe2x80x9cBlasenreaktorxe2x80x9d). In an airlift reactor it is in principle a matter of carrying out the liquid supplying (nutrient solution) and the likewise required supplying with gases such as e.g. oxygen in such a manner that bubbles rise in the liquid or are held there in flotation respectively.
In an exemplary embodiment of an airlift reactor of this kind the latter comprises a reaction container in which a hollow body is arranged, of which the jacket is connected at its lower end to the wall of the reaction container and tapers in the direction towards the upper end of the reaction container so that it subdivides the inner space of the reaction container into an upper chamber and a lower chamber. The upper and lower end side of the hollow body are designed to be liquid and gas permeable (e.g. as membrane) and enclose a cavity in which the substance to be acted upon (e.g. the cells or the micro carrier with the cells or the biodegradable matrix material with the cells) can be arranged. Depending on the kind of the employment however one or both membranes need not necessarily be present. The supply line for the liquid medium opens into the upper chamber and a suction device for the liquid medium is provided in the lower chamber. Through this a liquid flow is produced which comes from above and passes through the cavity in which the substance to be acted upon is arranged and into the lower chamber. A supply device for the gaseous medium is arranged in the lower chamber. This has the effect that the bubbles rise in the liquid. Since the speed of the liquid flow in the upper region of the cavity is however greater (smaller diameter) than in the lower region (greater diameter) the rising bubbles in the upper region are again taken along by the flow downwards where the flow speed of the liquid flow is again lower, for which reason the bubbles again begin to rise. Through a corresponding choice of the flow speed it is thus possible to xe2x80x9cconcentratexe2x80x9d the bubbles in the cavity in which the substance to be acted upon is arranged.
In a further development of an airlift reactor of this kind the reaction container is designed to be cylindrical and the hollow body is designed to have the shape of a truncated circular cone. In this the supply line opens into a preferably ring-shaped or circular areal distributor which is arranged in the upper chamber and surrounds the hollow body. The suction device for the liquid medium, which is arranged in the lower chamber, is likewise preferably designed to be ring-shaped or circularly areal. This yields on the one hand a well controllable flow and ensures on the other hand that the distributor as well as the suction device can also be used when the dimensions of the container and the hollow body which is arranged therein should happen not to correspond so precisely to the desired dimensions.
In a further exemplary embodiment of the airlift reactor the latter comprises a reaction container in which a hollow body is arranged, of which the jacket is connected at its upper end to the wall of the reaction container and which tapers in the direction towards the lower end of the reaction container so that it subdivides the inner space of the reaction container into an upper chamber and a lower chamber. The upper and lower end surface of the hollow body are in each case designed to be liquid and gas permeable (e.g. as a membrane or as a net or as a filter mat) and enclose a cavity in which the substance to be acted upon can be arranged. The supply line for the medium opens here into the lower chamber, with the gaseous medium already being admixed to the liquid medium (e.g. by means of an oxygenator). A suction device for the medium through which a desired flow speed can be produced is provided in the upper chamber. The flow speed is directed upwards, with it being the greatest in the lower region of the hollow body and decreasing upwardly through the widening of the hollow body. Through this the cells which are located between the two membranes are held in flotation, through which good conditions for the growth of a three-dimensional cell compound (tissue) result.
In another exemplary embodiment the reaction container can comprise a flexible pouch which can be inserted into a dimensionally stable reception. This reception can for example be designed as a thermal jacket and hold the temperature of the medium at a desired temperature. In addition the thermal jacket lends the required stability to the flexible pouch.
Finally, in all exemplary embodiments not only the pump and/or parts thereof are designed as expendable parts. In addition, all other constituents of the bioreactor which come into contact with the medium can also be designed as expendable parts. The bioreactor can thus already be delivered as an assembled bioreactor packed in a sterile condition which is replaced after each employment.
The essential idea of the invention is thus the use of an expendable pump or a pump with parts which are designed as expendable parts in a bioreactor, which however, as explained above, can be realized in many different manners. However, a bioreactor can also be used in an advantageous manner in which all parts which come into contact with the medium are designed as expendable parts. In this way a contamination in a second employment (which thus does not exist with the same bioreactor) is reliably avoided.
The artificial production of tissue material, often called xe2x80x9ctissue engineeringxe2x80x9d, is increasingly gaining in importance in order to produce biological substitutes for damaged tissue or damaged organs. Artificial tissue material can be produced in that cell cultures in vitro are deposited at or in a tissue carrier, also designated as a matrix. The tissue carrier consists for example of a synthetic polymer or of a biological material such as collagen. A tissue carrier of this kind is also designated as a xe2x80x9cscaffoldxe2x80x9d. The cells are sown out onto the tissue carrier and begin to multiply if the environmental parameters are physiologically favorable. The tissue carrier can be designed in such a manner that the latter disintegrates with time, so that after a certain time only the tissue part which is formed from the cells is present. The tissue carrier and/or the tissue part which is formed on it is designated as xe2x80x9csubstancexe2x80x9d in the following. The conditions which are required for the cell growth are produced in a bioreactor, within which the required oxygen and a nutrient medium are supplied to the substance and within which the substance remains from several days to weeks until the desired size has been reached. The geometrical shape which the artificially produced tissue material assumes during growth is substantially influenced through the measures by means of which the substance is held in the bioreactor.
Thus in the following the term xe2x80x9csubstancexe2x80x9d will be understood to mean both the tissue carrier per se and the tissue carrier with cells deposited on it, or, if the tissue carrier is designed to be decomposable, the artificially produced cell culture or the artificially produced tissue part respectively.
As a method for the holding in flotation of a substance in a bioreactor the substance is preferably acted upon with a fluid, with the flow of the fluid acting counter to gravitation in such a manner that the substance is held in flotation.
This method has the advantage that the substance is held without contact in the bioreactor in that the fluid, usually a liquid, has a flow which is developed in such a manner that the substance is held without contact by the flow, which acts counter to gravitation. In this the substance is usually also kept continually in motion so that its position changes continually. This method has the advantage that the cells grow uniformly at or in the substance respectively and the growth of the substance is favored. Disadvantageous in the previously known methods for the artificial production of tissue is the fact that it had been possible to produce only flat, substantially two-dimensional structures.
In a particularly advantageously designed method the fluid has an increasingly lower flow speed in the direction opposite to gravitation. This flow behavior is for example produced in that the flowing fluid is led from below into a hollow body having the shape of a truncated cone which widens upwardly. The cross-section of the hollow body, which widens upwardly, causes the flow speed in the hollow body to be reduced with increasing height. The substance is continually held in flotation in the inner space of the hollow body, with the side walls of the hollow body limiting a lateral movement of the substance, so that the substance is always located in the upwardly flowing liquid. With increasing cellular growth the weight of the substance increases, so that the substance moves slightly downwards in the inner space of the hollow body and finds again a new equilibrium position there. The substance thus automatically seeks the respective equilibrium position. It can however prove advantageous to monitor the position of the substance with a sensor and to influence the speed of the upwardly flowing fluid by means of the measured signal. Thus the speed of the fluid can for example be regulated in such a manner that the substance is continually held in flotation in a predetermined position.
In an advantageous method, in addition to the upward flow within the bioreactor a downward flow is also produced, with a gaseous fluid such as air or oxygen being supplied to the downwardly flowing fluid, usually a liquid. The speed of the downwardly flowing fluid is advantageously chosen such that the gaseous fluid which is input is slowed down or no longer rises at all, so that the gaseous fluid remains relatively long in the flowing fluid and can be taken up or absorbed respectively by the latter.
An advantageously designed bioreactor comprises a container for a substance which is to be acted upon with a fluid, with the container comprising a first flow chamber to which a flowing fluid can be supplied, and with the first flow chamber being designed in such a manner that the fluid which flows upwardly therein has a lower speed with increasing height. In a particularly advantageous embodiment the flow chamber has an upwardly widening cross-section.
In a further advantageous design a flow guiding means is arranged within the bioreactor and forms a flow chamber which widens upwardly. This flow guiding means preferably forms in addition within the bioreactor a further, second flow chamber which widens downwardly and into which a gaseous fluid can be led.
In a further, advantageous embodiment a drivable pump wheel is arranged within the bioreactor, with the help of which the flow of the fluid within the bioreactor can be produced. The pump wheel is advantageously magnetically coupled to a drive which is arranged outside the housing of the bioreactor. The bioreactor housing and the pump wheel are advantageously conceived as throw-away or expendable products respectively so that the latter can be disposed of after a single use. These parts can be manufactured economically. For example the pump wheel can comprise a vaned wheel of plastic into which a permanent magnet is cast. All expensive components such as the drive apparatus are arranged outside the bioreactor. The design of the bioreactor as an expendable product has the advantage that no laborious cleaning process is required and that a contamination of the artificially produced tissue material is largely excluded. The avoiding of a contamination is of decisive importance since the substance remains for example four to eight weeks in the bioreactor, until sufficient artificial tissue material has been formed. Since the bioreactor has no immune reaction system, the slightest contaminations such as bacteria, fungi or viruses can already result in the produced artificial tissue dying off or being contaminated. Through the design of the bioreactor as an expendable product, artificial tissue material can be economically and reliably produced.